This invention relates to the field of video signal processing, and in particular to time compression or time expansion.
It is often desirable in the television industry for the content received by a broadcaster to be shortened in time, either to reduce the video program length to fit a desired time slot, or to provide additional broadcast time into which revenue-generating commercials can be inserted. Typically, a video program will be reduced in length by up to four percent.
One commercially available product operates by identifying candidate fields in the uncompressed video sequence and deleting them. A candidate field might be one in which there is close similarity with the neighbouring fields.
Automated deletion of fields is cost effective but can introduce motion and other artefacts. The alternative exists of reediting the material but this is likely to be expensive and time-consuming.
The present inventors have recognised that it would be desirable to be able to provide this type of time compression (or in appropriate cases, time expansion) in the compressed domain, and particularly in compression schemes that utilise groups of pictures of differing prediction types, such as long Group of Pictures (GOP) structures in MPEG and other schemes.